Electronic devices such as a hard disk drive (HDD), a notebook personal computer, and a camcorder generally include acceleration sensors for detecting acceleration of the electronic devices and shock received by the electronic devices as a result of external force applied to the electronic devices. Such acceleration sensors may be formed of a piezoelectric material (i.e., a piezoelectric acceleration sensor). In the piezoelectric acceleration sensor, the acceleration of gravity acting on the piezoelectric acceleration sensor causes stress, electromotive force or electric charges are induced by the piezoelectric effect that results from the stress, and the acceleration of the piezoelectric acceleration sensor is detected by detecting the electromotive force or electric charges.
Examples of the piezoelectric acceleration sensors are disclosed in Japanese Laid-Open Patent Application Publication No. 2005-342817 (hereinafter called “Patent Document 1”), Japanese Laid-Open Patent Application Publication No. 2009-8512 (hereinafter called “Patent Document 2”), and Japanese Laid-Open Patent Application Publication No. 2002-162408 (hereinafter called “Patent Document 3”). The piezoelectric acceleration sensors disclosed in Patent Document 1 and Patent Document 2 utilize a cantilever transverse vibration d31 mode whereas the piezoelectric acceleration sensor disclosed in Patent Document 3 utilizes a substrate shearing vibration d15 mode.
Further, the sensor elements may increasingly need to be provided in various places for establishing a sensor network (or wireless sensor network). Micro-piezoelectric power generator devices utilizing piezoelectric micro-electro mechanical systems (MEMS) have attracted much attention as a power supply for such sensor elements. The micro-piezoelectric power generator devices are extremely small devices utilized as power converters that convert natural or artificial vibrations into energy. Since the size of the sensor elements are extremely small, the vibration power generator device that is a power source for the sensor elements may need to have high sensitivity in generating power.
[Patent Document 1] Japanese Laid-open Patent Publication No. 2005-342817
[Patent Document 2] Japanese Laid-open Patent Publication No. 2009-8512
[Patent Document 3] Japanese Laid-open Patent Publication No. 2002-162408
The electronic devices such as hard disk drives, notebook PCs and camcorders may be carried outdoors. Hence, the electronic devices may frequently be hit without being damaged. Further, the sensor elements establishing the wireless sensor network may also be carried outdoors or in vehicles, and they may sometimes receive strong vibrations. Accordingly, the acceleration sensors installed in these electronic devices may be expected to have sufficient toughness so as to be durable against such strong impacts. Since the acceleration sensor utilizing the cantilever transverse vibration d31 mode includes a cantilever configuration that has a susceptibility to shock or impact, the acceleration sensor may be broken due to the impact applied to the acceleration sensor. Further, since the acceleration sensor utilizing the substrate shearing vibration d15 mode is formed of a sheet-type piezoelectric material attached to the substrate and has high toughness, the acceleration sensor may have low sensitivity.
In view of the above-described factors, an acceleration sensor having high toughness and high sensitivity and a vibration power generator device for such acceleration sensor may be increasingly desired.